California allocates vastly more water than supplies allow, study shows

The state of California has handed out five times more water rights than nature can deliver, a new study by University of California researchers shows.

California’s total freshwater runoff in an average year is about 70 million acre-feet, according to the study. But the state has handed out junior water rights totaling 370 million acre-feet. One acre-foot is enough to meet the needs of two average households for a year.

The rivers under the most strain, the research indicates, are virtually all that drain into the Central Valley, including the Sacramento, Feather, Yuba, American, Mokelumne, Stanislaus, Tuolumne, Merced, Kings and San Joaquin rivers. Others near the top include the Salinas, Santa Clara, Santa Ana and Santa Ynez rivers.

“It seems clear that in a lot of these cases, we’ve promised a lot more water than what’s available,” said Ted Grantham, the study’s lead author, who conducted the research as part of postdoctoral studies at UC Davis. “There’s never going to be enough water to meet all of these demands.”

Help us deliver journalism that makes a difference in our community.

Our journalism takes a lot of time, effort, and hard work to produce. If you read and enjoy our journalism, please consider subscribing today.

The study confirms prior estimates of the disparity but goes further by describing the degree of over-allocation in individual watersheds across California. It also reveals that the problem may be much larger since the researchers looked at only a subset of California water rights – those allocated after 1914 and considered “junior” rights.

California’s system of water rights, overseen by the State Water Resources Control Board, is the primary means by which the state distributes natural runoff to provide water for cities, farms and industry. In most cases, a property owner or government agency applies to the state for a water right or permit. If granted, it allows them to divert a certain amount of water directly from a river or stream.

Such rights, for example, account for all the water stored behind dams in the state, which is the primary source of drinking water for many Californians and irrigation water for crops.

The study was published in the current issue of the journal Environmental Research Letters. It was conducted by analyzing more than 12,000 water rights issued after 1914, the year California adopted its system of water diversion rules. Only those rights had sufficient data available for analysis, Grantham said.

The researchers then used streamflow data collected by the U.S. Geological Survey to establish baseline natural runoff volumes for about 4,500 sub-watersheds across the state. These data were compared to the water rights. In many cases, the results showed that diverters are allowed to withdraw far more water than the stream can produce in an average weather year.

“In so doing, they give these rights-holders a false sense of water security,” said Joshua Viers, a co-author of the study and an engineering professor at UC Merced. “It’s an entitlement that may never be filled. That is unfortunate, because we continue to allocate water rights to this day.”

In dry years like this one, the disparity grows worse, because there is less snowmelt to feed streams. The consequences can be dire: This summer, the state water board imposed curtailments on about 10,000 water rights, requiring diversions to be halted completely because there isn’t enough water to go around.

Craig Wilson, Delta water master for the state board, has a different view of the situation. He said the excess allocation of water is “overblown” because many water-rights holders actually divert less water than their permits allow. And very often, much of that diverted water returns to the same stream as runoff from farm fields, where it can be used again by someone downstream.

“It’s very true, the board has issued water rights for more water than is available,” said Wilson, who oversees water rights in the Sacramento-San Joaquin Delta. “I don’t think it’s nearly as big an issue as some people believe.”

But Grantham said it is difficult to know for sure, because the state has no idea how much water is being diverted at any moment. Diverters are not required to report their water use in real time. Instead, they report water usage annually, and these reports are not verified for accuracy.

“Particularly in times of drought, I think there is just so much uncertainty in how these water rights are being exercised that it’s practically impossible to try and manage these systems,” said Grantham, who now works for the U.S. Geological Survey in Colorado.

Related stories from Sacramento Bee

It has long been assumed that correcting the excess allocation would be complicated because there are so many water rights, each with unique historical and legal complications. But Grantham said the study revealed that might not be so, because 80 percent of the water volume is held by 1 percent of the water rights, and mostly by government agencies.

“We don’t really need to deal with thousands and thousands of water-rights holders,” he said. “We might just need to deal with a couple hundred that hold 90 percent of the water.”